Metallurgy



3,329,537 METALLURGY James A. Loach, Vienna, W. Va., assignor to Kaiser Aluminum & Chemical Corporation, Oakland, Calif,

a corporation of Delaware No Drawing. Filed Sept. 6, 1963, Ser. No. 307,026 8 Claims. (Cl. 148-12.7)

This invention relates to a method for producing thermally treated metal sheets or plates.

Although the method of this invention is useful for treating different metals, it is particularly useful in the preparation of thermally-treatable aluminum sheets or plates, particularly the magnesium silicide aluminum a1- loys, to have desirable properties with a minimum of proc* essing steps.

Many commercial forms of aluminum, the term aluminum being used in this specification and the claims to in clude aluminum alloys, clad aluminum, etc., are pre pared by rolling aluminum ingots into sheets or plates. Although sheets are generally considered as being thinner than 0.250" while plates are considered as being 0.250" or thicker, the process of the present invention is applicable to both forms of aluminum, and wherever the word sheet is employed, the term plate may be substituted. It is also within the scope of this invention to emplov the process to the production of aluminum foils which are even thinner than sheets.

Thermally-treatable aluminum or heat treatable aluminum alloys are aluminum that contains alloying components which dissolve in the aluminum matrix at high temperatures but which precipitate from solution at lower temperatures. The precipitation of the alloying components is usually accompanied by hardening of the alloy and this precipitation is accordingly termed age-hardening. This phenomenon occurs at room temperature over a long period of time, but may be hastened by heating the alloy to temperatures in the range of ZOO-300 F. to accelerate age hardening so that it occurs within a few hours. The thermally accelerated process is called artificial age-hardening. The present invention is particularly useful in preparing alloys of aluminum, magnesium and silicon, however, with proper control of the process variables, difi'erent heat treatable alloys maybe employed.

Presently used conventional processes for producing aluminum heat treatable sheet material require first homogenization treatment of an aluminum body, such as an ignot, which is suitable for rolling into sheets. Homogenization is effected by heating the body to a temperature below the melting point but high enough to cause the alloying components to dissolve, and maintaining the ingot at that temperature for a long enough time for substantial portions of the principal alloying components to dissolve in the aluminum. Homogenizing temperatures vary from alloy to alloy, and are usually higher than about 850 F. The homogenized ingot is then hot rolled to sheet or plate of a gauge above that of the final thickness or to final thickness. The sheet is then cold rolled to substantially final thickness and finish. Although not essential, cold rolling is desirable to obtain the desired gauge and finish accurately. After cold rolling the sheet is cut to sizes larger than finish sizes and solution heat treated in air or salt bath furnaces. After quenching from the solution heat treatment, the sheet must be flattened, trimmed and otherwise prepared in final form. An artificial age period is then generally employed to provide it with the temper required for its ultimate use. The process hereinabove described is also employed with aluminum clad alloys which are produced by rolling an ingot having desirable physical properties between either one or two sheets of aluminum which is less 3,329,537 Patented July 4, 1967 subject to corrosion to provide a product that has the corrosion resistance of cladding and the physical properties of the core alloy.

At solution heating temperatures aluminum is soft, and when sheets formed by the conventional process are solution heated even the very light pressure of rollers in a solution heating oven and flexing of the plate and other necessary physical manipulations will mar or otherwise have an adverse effect upon the surface appearance. In fact, the ditficulty of maintaining the surface appearance of a finished sheet in its as-rolled condition has given rise to a great many devices for solution heating a sheet on its edge or on an air cushion. To obtain a bright finish on a conventionally produced sheet usually requires an added rolling step which is provided subsequent to the thermal treatments.

The present invention provides a process for producing sheet aluminum alloy which eliminates much of the troublesome thermal treating and greatly reduces the time, effort and expense of producing suitable sheet material from ingots. Additionally, the method of this invention is capable of producing sheet with an exception ally bright and uniform finish because no surface-marring solution heating need be effected subsequent to final finishing. Additionally, the process of this invention is capable of producing a sheet material heretofore not obtainable because the absence of solution heat treating after rolling results in a sheet with an exceptionally uniform surface.

The method of this invention includes preparing an aluminum body for rolling into sheet by solution heating the body and subjecting it to an initial rolling operation while it is at solution heating temperature, generally in excess of 850 F. but below the melting point of the alloy, at which temperature substantial portions of the primary alloying constituents are dissolved in the aluminum. The aluminum body may be pre-formed by casting, rolling, forging, etc., but the starting form for this invention is as a slab or ingot or other very thick body. The aluminum body is rolled at solution heating temperature to produce asheet which may be substantially thicker than the ultimately desired sheet generally less than times as thick as the ultimate product, but which is in the form of a sheet or plate. The sheet in this form is herein designated as a solution-heated sheet for purposes of this explanation.

Subsequent to rolling at homogenization temperature, the solution heated sheet is subjected to a combination of rolling and quenching, hereinafter called quench rolling. This portion of the process is effected by introducing the sheet while at solution heating temperature into one or a series of pairs of cooled rolls in which, simultaneously, the thickness of the sheet is reduced and the temperature of the sheet is reduced. Quenching may be accomplished with cooled rolls, spraying the sheet, forced air or by other conventional means. In one embodiment of this invention the thickness of the sheet is reduced to its final desired thickness and the final desired surface is placed on the sheet during the hot rolling portion of the process while the temperature is reduced from solution heating temperature to below 450 F. In another embodiment of this invention the quench rolling process is effected to reduce the thickness of the sheet to almost its final desired thickness while the temperature is reduced from solution heating temperature to below 450 F. The quench rolling portion of the process is then followed by a cold rolling process which reduces the thickness of the sheet to gauge and provides the finish surface on the sheet.

The sheet material that results may, if desired, be artificially age hardened either immediately after rolling or following a period of natural aging. The artificial aging,

as hereinbefore stated, is effected at temperatures below 300 P. which is substantially below the softening temperature of aluminum, and artificial aging does not affect the appearance of the aluminum sheet. Therefore, in the process of the present invention, if the sheet is finally finished with a bright mirror finish, the product retains its bright mirror finish and is usable for the production of products, such as vessels, trailer bodies, containers, etc., in this bright form. Similarly, textured finishes, such as matte finishes, grained finishes, etc., are subjected to no marring or other surface disfiguration but are sent to the consumer with exactly the finish that is provided by the rolling process. Regardless of the finish imparted to the product, the alloy has a surface characterized by a high degree of uniformity that is not attainable in products produced by prior art methods.

Following are examples embodying this invention which are presented here as illustrative of the invention. The examples are in no way intended as being limiting on the scope of the invention with regard either to the method of the invention that is demonstrated in each example or with regard to the materials suitable for use in the method.

A series of alloys was prepared having compositions as indicated in Table 1 below.

Alloy No. 1 was cast into an ingot '16 x 44 x 142 inches in size, had afiixed to the 44 inch surfaces slabs of a corrosion resistant alloy and the composite was preheated for 3 hours at a temperature of approximately 930 F. after which it was rolled into a slab 4.5 inches thick. The cladding aluminum was constituted of a maximum of 0.7% silicon plus iron, at maximum of 0.1% copper, a maximum of 0.1% manganese, a maximum of 0.1% magnesium, between 0.8 and 1.3% zinc, and a total of 0.15% other material with the balance aluminum. This slab was the aluminum body for the process of the present invention and the method of forming it is not of significance in the process of this invention as long as good metallurgical standards are observed. The slab was heated to and maintained at a temperature of approximately 940 F. for 12 hours and immediately positioned on a rolling mill. Rolling at solution heating temperatures was begun. At the start of the solution heating rolling period the temperature of the slab was 940 F. and during rolling the temperature was reduced from 940 F. to 920 F. while the thickness of the slab was reduced from 4.5 inches to 1.0 inch.

Immediately upon completion of the rolling, while the metal was at a temperaturee of 920 F., the 1 inch thick plate was introduced into a 5-stand 4-high quench rolling mill in which cooled rollers reduced the thickness of the material from 1.0 inch to 0.102 inch while the temperature was lowered to 360 F. Following quench rolling the sheet was introduced into a two-stand cold rolling mill in which its thickness was reduced first from 0.102 inch to 0.072 inch and then from 0.072 inch to a final gauge of 0.061 inch. The sheet material emerging from the cold mill had an exceptionally bright and uniform surface. The sheet was then subjected to artificial aging by maintaining it at a temperature of 275 F. for 6 hours after which it was cooled. The artificial aging period had no affect on the bright, uniform appearance of the surface of the sheet.

The material thus produced was found to have the following properties:

Ultimate strength, K s.i 47.3 Yield strength, K s.i 44.1 Elongation, percent in 2 inches 7.0 Bend radius, in sheet thicknesses 4.0

Example 2 Alloy 2 was cast into an ingot and prepared into a 4.5 inch thick slab by the method described with reference to alloy 1. The slab was heated to and maintained at 910 F. after which it was rolled to a thickness of 1 inch. The 1 inch slab was immediately introduced, at a skin temperature of 900 F., into a 5-stand quench roll mill in which its temperature was reduced to 430 F. while its thickness was reduced from 1.0 inch to 0.102 inch. Following quench rolling, the material was cold rolled in a two-stand mill to reduce its thickness from .102 inch to 0.061 inch after which it was artificially age hardened by maintaining it at 275 F. for 6 hours.

The material thus produced had an exceptionally bright, uniform surface and was found to have the following mechanical properties:

Ultimate strength, K s.i 38.7 Yield strength, K s.i 35.3 Elongation, percent in 2 inches 8.5 Bend radius, in sheet thicknesses 1.0

Example 3 Alloy 3 was cast into an ingot and prepared into a 4.5 inch slab by the method described in Example 1 and the slab was solution heated to and maintained at 930 F. for 12 hours. While at solution heating temperature, the slab was reduced from 4.5 inches thick to 1.0 inch thick and while the slab was at 930 F. it was introduced into the 5-stand quench roll mill wherein its temperature was reduced from 930 F. to 425 F. while the thickness was reduced from 1.0 inch to 0.102 inch. The resultant sheet was cold rolled as in Examples 1 and 2 and artificially aged at 275 F. for 6 hours. The resultant material had an exceptionally bright and uniform surface and was found to have the following mechanical properties:

Ultimate strength, K s.i 39.3 Yield strength, K s.i 35.4 Elongation, percent in 2 inches 8.0 Bend radius, in sheet thicknesses 2.0

Example 4 Alloy 4 was prepared into a 4.5 inch slab by the method described in Example 1 after which the slab was maintained at a temperature of 1000 F. for a period of 9 hours. While at 1000 F. the slab was reduced from 4.5 inches thick to 1.0 inch thick while the temperature was dropped from 1000 F. to 980 F. The slab was introduced into the S-stand quench roll mill at 970 F. and it was reduced from 1.0 inch to 0.102 inch while the ternperature diminished from 970 F. to 350 F. The resulttant material was subjected to cold rolling in the 2-stand mill to reduce its thickness from 0.102 inch to 0.061 inch after which it was artificially aged at 275 F. for 6 hours. The resultant sheet was found to have exceptionally bright and uniform surface and the following mechanical Bend radius, in sheet thicknesses 2.0

Example 5 Alloy 5 was clad and prepared into a slab 4.5 inches thick by the method as described in Example 1. The slab was heated to and maintained at 1000 F. for 9 hours, and rolled as in Example 1. While its thickness was reduced from 4.5 inches to 1.0 inch the temperature dropped from 1000 F. to approximately 960 F. The 1 inch thick plate was then introduced at a temperature of 945 F. into the 5-stand quench rolling mill wherein its thickness was reduced from 1.0 inch to 0.102 inch while the temperature was reduced from 945 F. to 370 F. The sheet was then cold rolled in the 2-stand cold rolling mill to a thickness of 0.061 inch and artificially aged at 275 F. for 6 hours. The resultant material had an exceptionally bright and uniform surface and it was found to have the following properties:

Ultimate strength, K s.i 42.0 Yield strength, K s.i 38.2 Elongation, percent in 2 inches 9.0 Bend radius, in sheet thicknesses 2.0

Example 6 Alloy 6 was prepared as sheet for use in making can ends and venetian blind slats. The alloy constituted as defined in Table 1 was cast into an ingot 16 x 34 x 142 inches, the ingot was preheated to 940 F. and rolled into a slab 4.5 inches thick. This slab constitutes the aluminum body that is the starting point of the process of this invention. The slab was heated to 980 F. and maintained at that temperature for 12 hours after which its thickness was reduced to 1.0 inch while the temperature dropped to 970 F. The slab was introduced at 950 F. into a 5- stand quench roll mill wherein its thickness was reduced- Ultimate strength, K s.i 56.4 Yield strength, K s.i 54.5 Elongation, percent in 2 inches 4.0

As stated above, the examples presented are for purposes of illustration rather than limitation. The broad scope of the present invention is capable of embracing many alloys other than the magnesium silicide alloys indicated above and for any specific alloy the process parameters will vary to accommodate the properties of the alloy involved. For example, solution heating temperatures vary with different alloys in that diiferent hardening constituents go into solution at different temperatures and a solution heating temperature suitable for one alloy may be above the melting point of another. Determining the solution heating temperature is within the skill of the art and not part of this invention and the invention and claims should not be limited thereby. Similarly, the temperature range of the quench rolling portion of the proc ess, the quenching rate, and the artificial aging and requirement for cold rolling will be determined on the basis of the particular alloy employed and the particular product desired. The amount of reduction at solution heating temperature, or conversely the thickness of the sheet when it neters the quench rolls in relation to the 6 final thickness will also be determined on the basis of the alloy characteristics and the amount of work imparted by quench rolling.

What is claimed is:

1. A method for producing aluminum sheet of a de sired thickness comprising:

(a) solution heating an aluminum body,

(b) rolling said body at solution heating temperature to produce a solution heated sheet, and

(c) passing the resultant solution heated sheet while at solution heating temperature through a series of cooled rolls wherein the thickness is reduced to said desired thickness while the temperature is reduced to below 450 F.

2. The method of claim 1 wherein the finished sheet is subjected to artificial age hardening.

3. The method of claim 1 wherein the final rolling produces a bright finish on said plate.

4. A method for producing aluminum sheet of a desired thickness comprising:

(a) solution heating an aluminum body,

(b) rolling said body at solution heating temperature to produce a solution heated sheet substantially thicker than said desired thickness,

(c) passing the resultant solution heated sheet while at solution heating temperature through a series of cooled rolls and reducing the thickness of said sheet to almost said desired thickness while simultaneously reducing the temperature of said sheet to below 450 F. to produce a hot rolled sheet, and

(d) cold rolling said hot rolled sheet at temperatures below 450 F. to said desired thickness.

5. The method of claim 4 wherein the finished sheet is subjected to artificial age hardening.

6. The method of claim 4 wherein the final rolling produces a bright finish on said plate.

7. A method for producing magnesium silicide aluminum alloy sheet of a desired thickness comprising:

(a) heating and maintaining a body of magnesium silicide alloy to temperatures of at least 900 F. until substantial amounts of the alloying constituents are in solution,

(b) rolling said body at solution heating temperature to produce a solution heated sheet, and

(c) passing the solution heated sheet at an initial temperature higher than 900 F. through a series of cooled rolls to reduce the thickness while cooling to below 450 F.

8. An aluminum sheet having an exceptionally uniform surface prepared by the method comprising:

(a) solution heating an aluminum body,

(b) rolling said body at solution heating temperature to produce a' solution heated sheet, and

(c) passing the resultant solution heated at solution heating temperature through a series of cooled rolls wherein the thickness is reduced to said desired thickness while the temperature is reduced to below References Cited UNITED STATES PATENTS 3,234,053 2/1966 Pryor 14811.5

DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, Examiner.

H. SAITO, Assistant Examiner. 

7. A METHOD FOR PRODUCING MAGNESIUM SILICIDE ALUMINUM ALLOY SHEET OF A DESIRED THICKNESS COMPRISING: (A) HEATING AND MAINTAINING A BODY OF MAGNESIUM SILICIDE ALLOY TO TEMPERATURES OF AT LEAST 900%F. UNTIL SUBSTANTIAL AMOUNTS OF THE ALLOYING CONSTITUENTS ARE IN SOLUTION, (B) ROLLING SAID BODY AT SOLUTION HEATING TEMPERATURE TO PRODUCE A SOLUTION HEATED SHEET, AND (C) PASSING THE SOLUTION HEATED SHEET AT AN INITIAL TEMPERATURE HIGHER THAN 900*F. THROUGH A SERIES OF COOLED ROLLS TO REDUCE THE THICKNESS WHILE COOLING TO BELOW 450*F. 